From the contemporary standpoints of environmental protection and space saving, it is strongly desired in the medical imaging field to reduce the quantity of spent solution. Needed in this regard is a technology relating to thermographic photosensitive materials for use in medical diagnosis and general photography which can be effectively exposed by means of laser image setters and laser imagers and produce distinct black images having high resolution and sharpness. These thermographic photosensitive materials offer to the customer a simple thermographic system which eliminates a need for solution type chemical agents and is not detrimental to the environment.
On the other hand, the laser technology is now on rapid progress and applied to medical image output devices. For example, the sensitizing technique is disclosed in U.S. Pat. No. 5,441,866 and the anti-fogging technique disclosed in JP-A 182639/1992.
Photothermographic materials are generally highly transparent and require addition of anti-irradiation dyes in order to maintain sharpness. The anti-irradiation dyes, however, tend to prohibit the adsorption of sensitizing dyes to silver halide, leaving the problem that the photo-sensitive material experiences a significant drop of sensitivity during long-term storage.